1. Field of the Invention
The present invention relates to thermoset resins. More particularly, the present invention relates to resin compositions displaying both a remeltable phase and a cured thermoset phase.
2. Description of the Prior Art
Thermoset melamine resins are widely used in the manufacture of laminates and as coatings for fibrous nonwoven webs. Typically, these resins are formed from the aqueous copolymerization of melamine and formaldehyde in a 1:1 to 1:3.5 ratio. Though these resins have achieved great acceptance in the art, several disadvantages still persist. Among the most problematic is the high level of volatile free formaldehyde that is emitted by this resin, both in its manufacture, and in final products made therefrom. Further, the formaldehyde and melamine resin components undergo rapid cross-linking once combined, reducing their flowability and/or sprayability unless immediately used. Accordingly, processes and apparatuses utilizing this class of resin are conventionally encumbered with at site preparation of the resin, in addition to applying the resin.
Improvements in the form of additives to the basic melamine/formaldehyde system have been a constant pursuit of the prior art. U.S. Pat. No. 3,532,647, issued Oct. 6, 1970 to Daniel D. Ritson et al. describes a coating composition that includes a &lt;C.sub.18 sugar, such as sucrose, as an extender in a melamine-formaldehyde resin.
Polyvinyl acetate and/or glycerol have also been used in prior art melamine/formaldehyde resin systems. For example, U.S. Pat. No. 4,018,966, issued Apr. 19, 1977 to George J. Antifinger et al. describes a polymer of various vinyl compounds, such as vinyl acetate, with a hydroxyl-containing monomer copolymerizable therewith and a thermosetting resin such as melamine/formaldehyde. The hydroxyl-containing monomer may be glycerol. U.S. Pat. No. 3,458,465, issued Jul. 29, 1969 to Kurt Rehnelt et al. describes a laminate binding solution that includes polyvinyl alcohol with residual acetyl groups (such as the acetate), a polyhydric alcohol (such as glycerol), and melamine. U.S. Pat. No. 3,936,547, issued Feb. 3, 1976 to Karl Schnee et al. incidentally describes that melamine resins, urea resins, and polyvinyl acetate dispersions alone or in combination may be used in self-adherent films (See col. 1, lines 13-25) U.S. Pat. No. 4,245,689, issued Jan. 20, 1981 to Henry P. Grard et al. describes a backing web that includes a binder component of, among others, vinyl acetate and stearylated melamine emulsion.
U.S. Pat. No. 4,499,125, issued Feb. 12, 1985 to Elmer P. Blasing et al. patent describes a solid or molten melamineformaldehyde resin that may be used in laminates. U.S. Pat. No. 5,368,803, issued Nov. 29, 1994 to Mark J. Brow et al. patent describes a method for producing melamine based resin panels with no odor and low levels of aldehyde release.
U.S. Pat. No. 4,898,696, issued Feb. 6, 1990 to Wolfgang Sliwka; U.S. Pat. No. 5,182,335, issued Jan. 26, 1993 to Mario Da Re'; U.S. Pat. No. 5,283,266, issued Feb. 1, 1994 to Satoshi Matsuo et al.; and Europe Patent Application No. 0 082 635 A1, published Jun. 29, 1983 and assigned to Appleton Papers, Inc. describe melamine encapsulation of various polymer and/or inert components.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.